Cathode structure having thermal expansion compensating means



United States Patent [72} Inventor William H. Nevins Stamford, Conn. [21] Appl. No. 646,602 [22] Filed June 16, 1967 [45] Patented Dec. 29, 1970 [73] Assignee The Machlett Laboratories, incorporated Springdale, Conn. a corporation of Connecticut [54] CATHODE STRllCTURE HAVING THERMAL EXPANSION COMPENSATING MEANS 6 Claims, 7 Drawing Figs.

[52] 0.8. CI 313/278, 313/285, 313/284, 313/257, 313/269 [51] Int. Cl l-[0lj 1/96, H01j 19/50; H01k1/18 [50] Field of Search, 313/284, 285, 278, 257, 269

[56] References Cited UNITED STATES PATENTS 2,923,848 2/1960 Weiss 313/278 I 7 so I3 35 1 [4 t 3,440,474 4/1969 Pawlikowski 313/278 3,312,854 4/1967 Finn 313/278 3,300,676 1/1967 Sterzl 313/278 3,299,310 1/1967 Freggens 313/278 3,026,442 3/1962 Lingers 313/278 3,124,713 4/1964 Randmer.... 313/271 2,602,907 7/1952 Shower 313/278 Primary ExaminerJohn W. Huckert Assistant ExaminerB. Estrin Auomeys- Harold A. Murphy and Joseph D. Pannone as g "2 r 88 9 t ms WCATHODE STRUCTURE nlwmc THERMAL EXPANSION COMPENSATING MEANS BACKGROUND or THE lNVENTlON This invention relates to an electrode structure for electron discharge tubes and is concerned more particularly with means for compensating for unequal thermal expansion in the cathode structure of high power discharge tubes. I

In order to obtain a compact structure for high power electron tubes, coaxially arranged electrodes are often used. High power tubes of the coaxial type usually comprise a cagelike filament structure concentric with the-longitudinal axis of the tube including a plurality of filament wires in a parallel, cylindrical arrangement and aconcentric, cag'elike grid having a wirewoundhelically around longitudinally extending support struts. The problem of maintaining uniform spacing between the directly heatedcathode and the closely spaced gridis complicated by the thermal expansion of the various parts due to the heat generated in high power applications-Even though means are provided for allowing thermal elongation of the filamentstrands, distortion of the filament structure can still occur because of unequal expansion and resulting thermal stresses in the'cathode structure supporting the filament cage.

In one coaxial type of power tube, the cylindrical array of parallel filament wires issupported at one end by two axially aligned discs. For purposes of electrical insulation, the discs are spaced apart, one being located closerto the filament wires then the other. Because the spaced, parallel discs have the appearance of a decklike structure, they'are commonly known as decks." Alternate filament wires connect to the support deck which is closer to the filaments. The other filament wires pass insulatingly through holes in the support deck 7 which is closer to the filaments and connect to the other support deck lt is important to maintain the original spacing between the support vdeckabecause the attached filament wires terminate at the other end in a common connecting member. If the spacing between the support decks, because the attached filament wires terminate at the other end in a common connecting member. If the spacing between the support decks is allowed to increase or'decrease, as'by thermal expansion or contractionduring the operation of the two the attached filament wires would be distorted out of cylindrical alignment and would alter the uniform interelectrode spacing between the filament and the grid. Therefore, the two filament support decks are usually mechanic'a lly locked together, in spaced relationship, by insulating means. In this manner, the positional relationshipiof the two support'decks to the attached filament wiresis maintained during operation of the tube in spite of thermal changes in the cathode support structure.

Each support deck is mounted on perpendicularly disposed supporting members which connect the support decks to cathode terminals. Besides conducting electrical current to and from the filament wires, the support decks and attached supporting members conduct heat outof the gastight envelope through the external connecting cathode terminals. The support deck adjacent to the heated filaments is exposed to a higher operating temperature and more radiant heat than the other support deck; and, therefore, mustdissipate more heat through the connected cathode terminal. The heat energy flowing from the support decks to the cathode terminals causes an increase in temperature and corresponding thermal elongation of the intervening deck supporting. members. The supporting members attached to the deck which is adjacent to the heated filaments undergo more thermal elongation than I the supporting members attached to the-deck remote from the. heated filaments. If one end of the respective deck supporting members is rigidly fixed to the respective cathode terminals,

the unequal thermal elongation of the respective supporting members is manifested at the other end attached to the perpendicularly disposed support decks. The support deck'adjacent the heated filaments tends to draw away from the other support deck, which would increase the-spacing between the decks. However, the mechanical interlocking means restrains the unequal thermal expansion from changing the spaced relationship of the two support decks. This restriction of thermal expansion sets up thermal stresses in the support deck adjacent the heated filaments which are transmitted to the at tached filament wires. The result can be distortion of the filaments and possibly permanent distortion of the support decks.

In the prior art, U. S. Pat. No. 2,521,714 discloses a means of compensating for unequal thermal elongation of the deck supporting members. However, the means provided also in troduces'an elementof mechanical distortion into the filament support structure. 'A cylindrical array of filament wires is supported at one end by two decks, one being closer to the filaments thanthe other. The two support decks are mechanically locked together by insulating means. The respective support decks are attached to respective support structures, each comprising a triangular shaped array of three, parallel supporting rods which are perpendicularly disposed to the support decks. The support deck which is closer to the filaments is connected directly to a cathode terminal by itsrespective support rods. The other support deck is connected to a parallel resilient disc by its respective support rods, which are attached to the disc adjacent the periphery thereof. The center of the resilient disc is rigidly fixed to a perpendicularly disposed cathode terminal. When unequal thermal elongation of the support rods tends to move the deck which is closer to the filaments away from the other deck, a pulling force will be exerted on the other deck through the mechanical interlocking means. This pulling force is transmitted through the attached support rods to the periphery of the resilient disc. Since the center of the disc is fixed rigidly to the cathode terminal, the resilient disc will flex in response to the pulling force at itsouter edge. Thus, the support rods attached to the resilient disc and the two interlocked support decks will be moved as a unit by the additional thermal elongation of the other set of support rods.

The disadvantage in using a resilient disc in the above application is that it cannot stretch radially to allow the attached ends of the support rods to move in a line perpendicular to the disc in its unflexed position. The support rods are attached perpendicularly to the disc at a fixed radial distance from the center of the disc, and the pulling force exerted by'each of the attached support rods is along the longitudinal axis of the rod. When-the disc is flexed, the attached ends of each support rod tend to move in a line coinciding with the longitudinal axis of the rod. However, the fixed radial distance of the attached rod ends from the center of the disc cannot elongate to permit perpendicular movement of the attached rods. Instead, the flexed disc assumes a dish-shape and the attached ends of the support rods are pulled radially inward toward the longitudinal axis of the structure. While the disc is flexing, the attached end of each support rod describes an are having a radius equal to the distance of the attached rod end from the center of the disc. The inward radial pull on the attached ends of the support rods tends to how the middle section of each support rod radially outward away from the longitudinal axis of the structure. This barrel-shape distortion of the support rods will exert a pulling force on the attached support deck and distort the cylindrical alignment of the connecting filament wires.

SUMMARY OFT HE INVENTION This invention provides a corrugated or bellowslike diaphragm of conductive metal which will stretch both longitudinally and radially to permit movement of an attached deck supporting member in response to a force produced by excess thermal elongation or contraction of the other deck supporting member. The capacity of the conductive bellows to stretch both radially and longitudinally avoids the mechanical distortion introduced by the prior art and constitutes an improvement provided by this invention.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of this invention, reference is made to the drawings wherein:

FIG. 1 is an axial sectional view of a typical coaxial type tube which may embody this invention;

FIG. 2 is an enlarged, fragmentary view in axial section of the hub cap assembly at the end of the center mast of the device shown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along line 3-3 of FIG. 1 looking in the direction of the arrows;

FIG. 4 is an enlarged cross-sectional view taken along line 4-4 of FIG. 1 looking in the direction of the arrows;

FIG. 5 is an enlarged fragmentary view in axial section of the insulating means that mechanically couples the filament support platforms;

FIG. 6 is an enlarged fragmentary view in axial section of the flexible diaphragm; and

FIG. 7 is an enlarged cross-sectional view taken along line 7-7 of FIG. I looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, wherein like characters of reference designate like parts throughout the several views, the tube embodying the invention as shown in FIG. 1 comprises a gastight envelope closed at one end by a deep, cylindrical anode cup 10 of highly conductive metal, such as copper, having an external annular flange 11, located adjacent its open end and providing the anode terminal. A metallic tubular member 12 is attached to the flange 11 at one end and at its other end is sealed to one end of a heavy dielectric cylinder 13.

Dielectric cylinder 13 and other dielectric parts used in this illustrative tube may be glass, ceramic or another vitreous material. Metallic tubular member 12 and other metal parts which seal to dielectric parts in this illustrative tube may be kovar or another material which readily seals to vitreous materials. Metal-to-metal sealing connections in this illustrative tube may be made by soldering, brazing or other convenient means.

A metallic, tubular member 14 is attached at one end to a circular seat adjacent the open end and inner diameter of anode 10. As illustrated, metallic tubular member 14 extends parallel to and beyond the end of metallic tubular member 12 to form a protective shield for the seal between metallic tubular member 12 and dielectric cylinder 13. The opposite end of dielectric cylinder 13 is sealed to one end of a metallic tubular member 15. The opposite end of tubular member 15 is attached to a dish-shaped metallic grid terminal 16 adjacent the perimeter thereof. In a central aperture of grid terminal 16 is mounted one end of metal sleeve 17 which extends inwardly of the envelope toward the anode cup 10, thus forming a protective shield for the seal between dielectric cylinder 13 and metallic tubular member 15. The opposite end of sleeve 17 supports an annular grid-supporting deck 18. A metal cylinder 19, which is concentric with the longitudinal axis of anode 10, is attached to annular grid deck 18 by any convenient means, such as screws 20. Metal support struts 21 are attached, as by welding, to cylinder 19 at spaced intervals around the circumference thereof and extend longitudinally into the interior of anode cup 10 to form a spaced concentric cylindrical configuration therewith. A grid wire 22 is wound helically around and is attached, as by welding, to the longitudinally extending struts 21. Attached to the opposite ends of struts 21 is a dishshaped metallic disc 23.

A center mast 30 terminates at one end in an assembly indicated generally as 3] which, as shown more clearly in FIG. 2, comprises hub cap type metal nut 32 threaded onto the end of the center mast 30 to bear against a metal cap washer 33 to press a dielectric washer 34 and a metallic filament support member 35 against a dielectric bushing 36. The opposite end of bushing 36 presses a metallic cap washer 37 against the end of a tubular sleeve 38 which surrounds the center mast 30.

As shown in FIG. 2, the dish-shaped cap 23 has a central aperture 24, the periphery of which surrounds but is spaced from the hub cap nut 32. Central aperture 24 is dimensioned such that the periphery thereof is slightly closer to hub cap nut 32 than the interelectrode space between the grid cage and the filament cage. In the event of mechanical shock, the periphery of the central aperture 24 will strike the hub cap nut 32 before the grid can contact the filament strands, thus preventing damage to the filament wires and the grid wire.

The thin metallic filament-support member indicated as 35 in FIG. 1 and FIG. 2 is shown more clearly in FIG. 3. Filament support 35 is disc-shaped and is perpendicularly disposed to center mast 30. A central aperture 39 is slightly larger than the shank diameter of dielectric bushing 36 which it slidingly engages. Filament support member 35 comprises a central hub portion from which arms 41 extend radially outward to attach to the bight portions of U-shaped filament wires 42. The free ends of the spokelike arms 41 attach to the filament wires 42 in a pivotal manner. Preferably, the extreme end of each metallic arm 41 folds around the bight portion of a respective U-shaped filament wire 42. The radial arms 41 flex easily so that filament wires 42 can elongate and retract during operation of the tube. The fixed length of arms 41 restrains the filament wires 42 from moving radially toward the grid cage. Thus, radial arms 41 offilament support 35 permit axial movement but restrain outward radial movement of the filaments. Filament strands 42 are supported in a parallel cylindrical arrangement to form a cagelike structure around the longitudinal axis of center mast 30.

As shown in FIG. 1, intermediate the ends of the center mast 30, the filament strands 42 come into contact with a spider comprising two spaced disc-shaped member 43 and 44 which are perpendicularly affixed to center mast 30 at different axial levels. Disclike members 43 and 44 are insulated from each other and insulatingly affixed to center mast 30 in a manner described in U. 5. Pat. NO. 2,659,023, issued to George J. Agule and assigned to the assignee of this invention. As shown in FIG. 4, discs 43 and 44 have central hub portions provided with radially extending clips 47 and 48, respectively, which project radially therefrom. Fine wires 49 and 50 extend radially from each respective clip 47 and 48, loop around a respective filament strand, and return to the same clip. Alternate filament strands are slidingly engaged by wire loops 49 and the other filament strands are slidingly engaged by wire loops 50. The advantage of using the wires 49 and 50 is that they prevent the middle sections of the filament strands from bowing out and touching the grid; and yet they allow the filament strands to move axially during operation of the tube.

The ends of the U-shaped filaments 42 are connected to clips 51 (FIG. I) which extend outward from connecting rods 52. Each of the connecting rods 52 isin parallel alignment with one of the filament strands 42. Thus, connecting rods 52 form a cylindrical array, perpendicular to two support decks 60 and 61. Alternate connecting rods are attached to support deck 60. The other connecting rods pass freely through apertures 62 in support deck 60, spaced from the periphery thereof, and are attached to support deck 61. The end of center mast 30 is attached to deck 60 by any convenient means, as by joumaling the center mast into an internally threaded hole through the center of the deck. Connecting rods 52 may be attached to the decks 60 and 61 by any convenient means, such as by soldering or brazing the ends of the rods into a properly aligned circular array of holes in the support decks.

Decks 60 and 61 are mechanically locked together by insulating means 63, such as that shown more clearly in FIG. 5. Three metallic rods 64 are attached to deck 61 at intervals around an imaginary circle that is concentric with the longitudinal axis of the tube. Rods 64 may be attached to deck 61 by any convenient means as by brazing them into bored holes or by joumaling them into threaded holes. A dielectric washer 65 is placed over each rod 64 between the decks 61 and 60, deck 60 being provided with three holes 66 which align with the rods 64 and have a diameter smaller than that of dielectric washer 65. A second dielectric washer 67 is mounted on each rod 64 and fits within hole 66. A third dielectric washer 68 is mounted on each rod 64 to rest against the opposite surface of support deck 60. A metal washer 69 is mounted against dielectric washer 68 and a metal nut 70 is threaded onto the projecting end of each rod 64 to bear against washers 69. Thus, there is provided in this embodiment of the invention a means for mechanically attaching deck 60 to 61 in a manner that electrically insulates them from one another.

Referring to FIG. 1 and to FIG. 7, a support cylinder 71 has one end provided with castellations 72 which protrude, in spaced relation, through radial slots 73 in support deck 61 and attach to deck 60. The opposite end of cylinder 71 is secured to a cathode terminal 74 which is attached to grid terminal 16 through a cylindrical sealed assembly comprising a metal sleeve 75, a dielectric sleeve 76 and a second metal sleeve 77.

From the preceding description, it can be seen that support deck 60 is nearer the heated filaments than support deck 61,

and hence is required to dissipate more heat than deck 61. Therefore, deck 60 is directly connected to cathode terminal 74 by means of outer, concentric cylinder 71.

One end of an inner concentric support cylinder 78 is attached to support deck 61, and the opposite end is circumferentially fastened to the periphery of central aperture 79 in flexible bellows 80. Bellows 80 comprises a series of radially extending thin metallic diaphragms 81, 82 and 83 (FIG. 6). Although only three are shown by way of example, any number of diaphragms may be used. The outer perimeter of bellows 80 is attached to a tubular member 84 which is mounted at the opposite end on cathode terminal 85. Cathode terminal 85 is attached to the other cathode terminal 74 through a sealed assembly of supporting members comprising metal sleeve 86, dielectric sleeve 87 and metal sleeve 88. The terminals and sealed assemblies complete the structure of the gastight envelope of the tube embodying the invention. A tubular pinch-off or exhaust tubulation 89 may conveniently be provided in cathode terminal cap member 85 for exhausting and vacuum sealing the gastight envelope.

From the foregoing description, it is apparent that any additional thermal elongation of supporting cylinder 71 over that sustained by support cylinder 78 will cause deck 61), to exert a pulling force on support deck 61 through the dielectric connecting means shown in FIG. 5 of the drawing. The pulling force on platform 61, transmitted through support cylinder 78, will act on the center of flexible bellows 80 around the periphery of central aperture 79. Bellows 80 expands radially and stretches longitudinally. Thus, cylinder 78 and support deck 61 can move along the longitudinal axis of the cathode structure without distortion. In this manner, cylinder 78 and attached deck 61 can mechanically follow the longitudinal movement of dielectrically attached deck 60 in response to the unequal thermal elongations or contractions of cylinder 71. Thus, support platform 60 and support platform 61 will maintain their original spaced relationship without distortion of the attached filament wires 42.

Essentially, the improvement provided by the expansible body of material, such as corrugated bellows 80, for example, lies in the fact that there is surplus material between the portion connected to the movable member, such as cylinder 78, and the fixed member, such as tubular member. 84. This enables the expansible body of material to have an expansion path which is greater than the distance between points of connection on the body in its relaxed state. The surplus material allows the resilient, corrugated diaphragm or bellows 80 to stretch radially and longitudinally for permitting relative motion between the mechanical movable deck supporting cylinder 78 and the fixed but thermally elongating deck supporting cylinder 71.

Althoughthe above description has been related to a particular embodiment of the invention, it will be apparent that one skilled in the art may make modifications in structure, such as the number or shape of the bellows, or in application, such as to indirectly heated cathode tubes, without departing from the spirit and scope of the invention as expressed in the appended claims.

' lclaim:

1. A cathode structure for an electron tube comprising:

first and second support members rigidly connected together in electrically insulated relationship;

a filamentary electrode adjacent said first support member and having one end portion mounted thereon, an opposed end portion of the electrode mounted on said second support member;

first and second terminal means spaced from said supporting members;

first electrically conductive means connecting said first support member to said first terminal means; and

second electrically conductive means connecting said second support member to said second terminal means comprising a rigid cylindrical body mounted on the second support member and expansible means having one point thereof connected to the rigid body and another point thereof connected to said second terminal means, said expansible means comprising a corrugated annular diaphragm which encircles the cylindrical body and is in contact with said body throughout the inner periphery thereof and is supported by said second terminal means at its outer periphery and having an expansion path greater than the distance between the points of connection for permitting relative motion between the rigid cylindrical body and the second terminal means in response to thermal expansion and contraction of said first electrically conductive means.

2. A cathode structure for an electron tube comprising:

first and second overlying support members rigidly connected together in electrically insulated relationship;

a filamentary electrode adjacent said first support member and having one end portion mounted thereon, an opposed end portion of the electrode mounted on said second support member;

first and second terminals spaced from said supporting members;

first electrically conductive means connecting said first support member to said first terminal; and

second electrically conductive means connecting said second support member to said second terminal comprising a rigid cylindrical body mounted on the second support member and expansible means having one point thereof connected to the rigid body and another point thereof connected to said second terminal, said expansible means comprising a corrugated annular diaphragm which encircles the cylindrical body and is in contact with said body throughout the inner periphery thereof and is supported by said second terminal at its outer periphery and having an expansion path greater than the distance between the points of connection for permitting relative motion between the rigid cylindrical body and the second terminal in response to thermal expansion and contraction of said first electrically conductive means.

3. A cathode structure as set forth in claim 2 wherein said first electrically conductive means comprises a first hollow cylinder, and said cylindrical body comprises a second hollow cylinder disposed in spaced concentric relation within and of greater length than said first cylinder.

4. A cathode structure as set forth in claim 1 wherein said filamentary electrode comprises a plurality of parallel wires arranged in a cylindrical configuration, each of the respective ends of said wires being mounted on respective support members.

5. A cathode structure as set forth in claim 4 wherein a hub is disposed at the opposite end of said filamentary electrode, said hub having radially extending flexible arms connected at their outer ends to respective parallel wires and movable in response to thermal elongation and contraction thereof.

6. A cathode structure as set forth in claim 4 wherein said. 

